1. Field of the Invention
The invention relates to polymer-bonded artificial stone, to a method for the production thereof, and to crosslinkable compositions used therefor which are based on organosilicon compounds.
2. Description of the Related Art
Artificial stone consisting of organic polymer resins crosslinkable with suitable catalysts, and fillers such as substances comprising silicon dioxide (quartz, quartzite, granite, porphyry, sand, silicates, clays, etc.), substances comprising calcium carbonate (marble, limestone, dolomite, etc.), substances comprising calcium or barium sulfate, aluminum oxide, aluminum trihydrate, magnesium oxide, magnesium hydroxide, zinc oxide and silicon carbide, and methods for the production thereof, have been known for a long time. Examples thereof are to be found in U.S. Pat. No. 4,643,921 and in the documents mentioned as prior art, which are likewise to form part of the disclosure of the present specification.
The polymer resin base used thereby, for example in “Bretonstone®” or Silestone® technology, is a radically crosslinkable polyester resin in combination with a reactive solvent such as styrene or methyl methacrylate or mixtures thereof. Reference is made in this connection, for example, to U.S. Pat. No. 4,698,010 and ES-B 2 187 313.
Furthermore, there are methods for producing artificial stones which comprise, instead of the polyester resin, methacrylate resins, as described, for example, in document US-A 2011/0 207 849, wherein the documents mentioned as prior art in that document are likewise to form part of the disclosure of the present specification for the mentioned organic polymer resin binders based on polyester resin or methacrylate resins.
A disadvantage of all the artificial stone known hitherto is that the binders have only limited stability to UV radiation and weathering. This is outwardly visible because—in particular in the case of dark color shades—the colors of the artificial stones become significantly lighter and, in addition, they lose their sheen. Furthermore, the polymer matrix is not stable to heat, that is to say the polymers depolymerize with pronounced discoloration. Moreover, the cured organic polymer matrix, despite high filler content, is flammable and sometimes burns with a very sooty flame.
Filled compositions based on organosiloxanes are likewise described in the literature. DD-A 103 252, for example, claims a method for producing molding compositions based on silicone resins in admixture with linear organopolysiloxanes. DE-A 2 504 357 describes silicone resin molding compositions, the crosslinkable resin base of which is composed of organopolysiloxane having at least 1.0% by weight silicon-bonded OH groups and a linear diorganopolysiloxane having OH or triorganylsilyl end groups. U.S. Pat. No. 3,108,985 claims phenylalkylsiloxanes as the resin base. It is a disadvantage in all these cases that, despite high curing temperatures, only comparatively low hardnesses of the test specimens are achieved. In addition, harmful lead compounds are used as the catalyst.
Furthermore, in DE-A 102 61 917 molded bodies are produced on the basis of a two-component addition-crosslinking silicone material which comprises short-chained vinyl-terminated siloxanes and hydrogen siloxanes as crosslinkable components and a platinum catalyst. Compositions having a filler content of up to 75% are described. It is a disadvantage that higher degrees of filling cannot be achieved without the processability being impaired and the mechanical properties diminishing very greatly.